The present invention relates generally to electronic circuits. More particularly, embodiments of the present invention relate to the field of integrated oscillator circuits for controllers and, in particular, controllers for ultra-low power battery applications.
FIG. 1 is a simplified block diagram illustrating a system 100 in which a controller is configured for frequent power-on and power-off operations. In this example, the (micro)-controller circuit is in a power down state, while it monitors the state of a terminal GPIO1. In this example, GPIO1 is connected to a temperature actuated switch 110, which trips at a preset temperature. An LED (light-emitting-diode) 120 is used to indicate when the temperature actuated switch has tripped, based on operations performed by the controller core. When the temperature actuated switch trips, the logic powers up the controller and enables the oscillator, which provides signals to the core logic to compute the LED driver function. When the computation is completed, the controller goes back to the power down state and shuts down the oscillator. Since the function requires the oscillator to power up and down frequently, it is desirable to have a fast power up and power down time in order to reduce power consumption. Further, the oscillator circuit needs to be a low power circuit in order to save power and extend battery life.
In addition, integrated circuit oscillators are also used to provide clock signals and ramp signals (or sawtooth signals) in pulse width modulation (PWM) based systems, such as those used in switch mode power supplies (SMPS) and amplifier circuits.
Some conventional integrated circuit oscillators use ring oscillators with precision external voltage and current references. Other conventional integrated circuit oscillators use capacitor charging circuit, but also rely on external reference circuits and control circuits.